ETSI ETS 300 223 ed.1 (1993-01)

SLOVENSKI STANDARD
01-december-2003
Terminalska oprema (TE) – Skladenjski Videotex – Splošni protokoli konec-konec
Terminal Equipment (TE); Syntax-based videotex protocol; Common end-to-end
protocols
Ta slovenski standard je istoveten z: ETS 300 223 Edition 1
ICS:
33.160.99 Druga avdio, video in Other audio, video and
avdiovizuelna oprema audiovisual equipment
35.180 Terminalska in druga IT Terminal and other
periferna oprema IT peripheral equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN ETS 300 223
TELECOMMUNICATION January 1993
STANDARD
Source: ETSI TC-TE Reference: DE/TE-01013
ICS: 33.040.40
Key words: Videotex
Terminal Equipment (TE);
Syntax-based Videotex;
Common end-to-end protocols
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
F-06921 Sophia Antipolis CEDEX - FRANCE
Postal address:
650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
Office address:
c=fr, a=atlas, p=etsi, s=secretariat - secretariat@etsi.fr
X.400: Internet:
Tel.: +33 92 94 42 00 - Fax: +33 93 65 47 16
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the
foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1993. All rights reserved.
New presentation - see History box

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ETS 300 223: January 1993
Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Editing and Committee Support Dept." at the address shown on the title page.

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ETS 300 223: January 1993
Contents
Foreword .9
1 Scope .11
2 Normative references.11
3 Definitions and abbreviations .12
3.1 Definitions .12
3.2 Abbreviations .14
4 Overview .15
4.1 Direct selection of Videotex applications .15
4.2 Multi-communication.15
4.3 Multi-media communication.15
4.4 Distributed Videotex application.16
4.5 Supplementary services.16
4.6 Handling of incoming calls .16
5 Configurations .16
6 General model.16
6.1 Communication model.17
6.2 Terminal model.18
6.3 Protocol pillar .22
7 Service definition .23
7.1 Introduction .23
7.2 Kernel services .25
7.2.1 SBV_Establish.25
7.2.2 SBV_Release .27
7.2.3 SBV_Reset.28
7.2.4 SBV_VTX_Data.28
7.2.5 CCITT Recommendation X.3 parameter manipulation services.29
7.2.5.1 SBV_Set_Param.29
7.2.5.2 SBV_Read_Param .29
7.2.5.3 SBV_Set_Read_Param.29
7.2.5.4 SBV_Param_Ind.30
7.2.6 SBV_TFI .30
7.2.7 SBV_TC_Error .30
7.3 Optional services .31
7.3.1 Communication channel management services .31
7.3.1.1 SBV_Channel_Open .31
7.3.1.2 SBV_Channel_Close.33
7.3.1.3 SBV_Channel_Error.34
7.3.2 Application selection services .35
7.3.2.1 SBV_Begin_Application.35
7.3.2.2 SBV_End_Application.35
7.3.2.3 SBV_End_Immediate .36
7.3.3 Transparent processable data services .36
7.3.3.1 SBV_TPD_Begin .36
7.3.3.2 SBV_TPD_End.37
7.3.4 SBV_DFK .37
7.3.5 SBV_Remote_Echo .37
7.3.6 SBV_Escape .38
8 Protocol .38

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8.1 Association of SBV Application layer and BIS primitives . 38
8.2 Procedures. 39
8.2.1 SBV_Establish . 40
8.2.2 SBV_Release . 40
8.2.3 SBV_Reset . 40
8.2.4 SBV_VTX_Data. 40
8.2.5 CCITT Recommendation X.3 parameter manipulation services . 40
8.2.5.1 SBV_Set_Param. 40
8.2.5.2 SBV_Read_Param. 40
8.2.5.3 SBV_Set_Read_Param . 40
8.2.5.4 SBV_Param_Ind . 41
8.2.6 SBV_TFI . 41
8.2.7 SBV_TC_Error. 41
8.2.8 Communication channel management services. 41
8.2.8.1 SBV_Channel_Open. 41
8.2.8.2 SBV_Channel_Close . 41
8.2.8.3 SBV_Channel_Error. 41
8.2.9 Application selection services. 41
8.2.9.1 SBV_Begin_Application . 41
8.2.9.2 SBV_End_Application . 41
8.2.9.3 SBV_End_Immediate. 42
8.2.10 Transparent processable data services. 42
8.2.10.1 SBV_TPD_Begin. 42
8.2.10.2 SBV_TPD_End . 42
8.2.11 SBV_DFK . 42
8.2.12 SBV_Remote_Echo. 42
8.2.13 SBV_Escape. 42
8.3 Mapping of parameters . 42
8.3.1 SBV_Establish . 43
8.3.2 SBV_Release . 43
8.3.3 SBV_Reset . 44
8.3.4 SBV_VTX_Data . 44
8.3.5 CCITT Recommendation X.3 parameter manipulation services . 44
8.3.5.1 SBV_Set_Param. 44
8.3.5.2 SBV_Read_Param. 44
8.3.5.3 SBV_Set_Read_Param . 45
8.3.5.4 SBV_Param_Ind . 45
8.3.6 SBV_TFI . 45
8.3.7 SBV_TC_Error. 45
8.3.8 Communication channel management services. 46
8.3.8.1 SBV_Channel_Open. 46
8.3.8.2 SBV_Channel_Close . 46
8.3.8.3 SBV_Channel_Error . 46
8.3.9 Application selection services. 47
8.3.9.1 SBV_Begin_Application . 47
8.3.9.2 SBV_End_Application . 47
8.3.9.3 SBV_End_Immediate. 47
8.3.10 Transparent processable data services. 47
8.3.10.1 SBV_TPD_Begin. 47
8.3.10.2 SBV_TPD_End . 48
8.3.11 SBV_DFK . 48
8.3.12 SBV_Remote_Echo. 48
8.3.13 SBV_Escape. 48
9 Coding .48
9.1 Coding of the Telematic Command PDUs . 48
9.2 Coding structures . 50
9.2.1 Basic coding structure . 50
9.2.2 Extended coding structure . 51
9.2.3 Coding of data types . 51
9.2.3.1 Integers . 51
9.2.3.2 Strings . 51
9.2.3.3 Voids . 52

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9.2.3.4 Octet sequences .52
9.3 Coding of parameters .52
9.3.1 Coding of user data fields using the coding structures .52
9.3.2 Coding of user data fields as defined in other documents .53
9.3.3 Service specific coding.54
9.3.3.1 Coding of the Error_Code parameter .54
9.3.3.2 Coding of the DDU_Fall-Back_Mode parameter.56
9.3.3.3 Coding of the Function_Keys parameter .56
10 Use of CCITT Recommendation X.3 parameters .60
10.1 Selectable functions provided by Syntax-based Videotex Terminals .60
10.2 List of X.3 parameters.60
11 Bearer Independent Service (BIS) for Syntax-based Videotex .61
11.1 Introduction .61
11.2 Scope and field of application.61
11.3 General operation of the BIS .63
11.3.1 Out-Band procedures for environment-dependent operation.63
11.3.2 Translation of primitives and parameters of In-Band procedures .64
11.4 Service primitives and parameters .64
11.4.1 Network Connection (NC) establishment primitives and parameters .65
11.4.1.1 Association of primitives and parameters.65
11.4.1.2 Parameter definitions.65
11.4.2 NC release primitives and parameters.66
11.4.2.1 Association of primitives and parameters.66
11.4.2.2 Parameter definitions .66
11.4.3 Unqualified data transfer primitives and parameters.67
11.4.3.1 Association of primitives and parameters.67
11.4.3.2 Parameter definitions.67
11.4.4 Qualified data transfer primitives and parameters .67
11.4.4.1 Association of primitives and parameters.67
11.4.4.2 Parameter definitions.68
11.4.5 Interrupt data transfer primitives and parameters .68
11.4.5.1 Association of primitives and parameters.68
11.4.5.2 Parameter definitions.68
11.4.6 Reset primitives and parameters .68
11.4.6.1 Association of primitives and parameters.68
11.4.6.2 Parameter definitions.68
11.4.7 Relation of primitives at the two NC endpoints.69
11.4.8 Sequence of primitives at one NC endpoint.70
11.5 Elements of the CCITT Recommendation X.25/PLP used to support the BIS.72
11.5.1 Types of virtual circuits.72
11.5.2 Packets and fields of the CCITT Recommendation X.25/PLP used to
support the BIS.72
11.5.3 Facilities of the CCITT Recommendation X.25/PLP used to support the
BIS.73
11.6 Network connection establishment phase .73
11.6.1 Primitive/parameter and packet/field relationships.74
11.6.2 Procedures.74
11.6.2.1 General Function .74
11.6.2.2 Primitive/packet mapping .74
11.6.2.3 Addresses.75
11.6.2.4 User data .75
11.7 Network connection release phase.75
11.7.1 Primitive/parameter and packet/field relationships.75
11.7.2 Procedures.76
11.7.2.1 General Function .76
11.7.2.2 Primitive/packet mapping .76
11.7.2.3 Originator and reason .76
11.7.2.4 Addresses.77
11.7.2.5 User data .77
11.8 Data transfer phase - (unqualified) data transfer service .77
11.8.1 Primitive/parameter and packet/field relationships.77

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11.8.2 Procedures . 77
11.8.2.1 Primitive/packet mapping. 77
11.8.2.2 User data. 78
11.9 Data transfer phase - qualified data transfer service (Q-bit=1). 78
11.9.1 Primitive/parameter and packet/field relationships. 78
11.9.2 Procedures . 78
11.9.2.1 Primitive/packet mapping. 78
11.9.2.2 User data. 78
11.10 Data transfer phase - reset service. 79
11.10.1 Primitive/parameter and packet/field relationships . 79
11.10.2 Procedures .79
11.10.2.1 General function . 79
11.10.2.2 Primitive/packet mapping . 79
11.10.2.3 Originator and Reason parameters. 80
11.11 Data transfer phase - interrupt transfer service . 80
11.11.1 Primitive/parameter and packet/field relationships. 80
11.11.2 Procedures . 81
11.11.2.1 Primitive/packet mapping. 81
11.11.2.2 User data. 81
Annex A (informative): Examples of configurations.82
A.1 Symbols . 82
A.2 Access to PSTN/PSPDN systems using a terminal adaptor . 82
A.2.1 Analogue terminal adaptors . 82
A.2.2 Rate adapting terminal adaptors . 82
A.3 Connection to a Videotex Service via ISDN . 82
A.4 Access to a Videotex Service via a ISDN/PSPDN. 83
A.5 Access to a Videotex Service via an ISDN Syntax-based Video Access Point. 84
A.5.1 Service selection after a dialogue with the IVAP. 84
A.5.2 Service selection using a Videotex Service identification. 85
A.5.2.1 Videotex Service identified by a network address . 85
A.5.2.2 Videotex Service identified by a name. 85
A.5.3 Service selection using ISDN supplementary services . 85
A.5.4 Distributed Videotex Application. 86
A.5.4.1 Usage of a single Virtual Call between an ISDN Syntax-based Virtual
Terminal and IVAP. 86
A.5.4.2 Establishment of the second VC by the IVT . 87
A.5.4.3 Establishment of the second VC by the IVAP. 87
A.6 Host to terminal call establishment. 88
A.7 Terminal to terminal communication . 88
Annex B (informative): Usage of supplementary services. 89
B.1 User-to-User Signalling (UUS). 89
B.2 Supplementary services for addressing . 89
B.2.1 Multiple Subscriber Number (MSN) . 89
B.2.2 Direct Dialling In (DDI). 89
B.2.3 Subaddressing (SUB).89
B.2.4 Call Deflection (CD). 89
B.3 Supplementary services for identification . 90
B.3.1 Calling Line Identification Presentation (CLIP). 90
B.3.2 Calling Line Identification Restriction (CLIR). 90
Annex C (normative): Terminal Function basic state. 91

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C.1 CCITT Recommendation X.3 parameter default values .91
C.2 SBV_DFK Default List.91
C.3 SBV_TPD default state .91
C.4 SBV_Escape default state.91
Annex D (informative): The SBV_Escape service.92
D.1 Service description.92
D.1.1 Bulk Update .92
D.2 Procedures .92
D.2.1 Bulk Update .92
D.3 Coding .93
Annex E (informative): Extended data forwarding signals .94
Annex F (normative): BIS constraints on ISO 8208 PICS.95
F.1 Introduction.95
F.2 Tables structure .95
F.3 Constraints tables.96
F.3.1 Virtual circuit types.96
F.3.2 Call setup.96
F.3.3 Call clearing .96
F.3.4 Resetting of logical channels .96
F.3.5 Normal data transfer and flow control.97
Annex G (informative): Bibliography.98
History.100

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Foreword
This European Telecommunication Standard (ETS) has been produced by the Terminal Equipment (TE)
Technical Committee of the European Telecommunications Standards Institute (ETSI).
Annexes C and F to this ETS are normative whereas Annexes A, B, D, E and G are informative.
NOTE: Abstract testing requirements for the Syntax-based Videotex end-to-end protocols are
currently being developed by ETSI (see final draft prI-ETS 300 236).

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ETS 300 223: January 1993
1 Scope
This ETS specifies both the end-to-end Application layer protocol for the Syntax-based Videotex Service
(VS) and the underlying Bearer Independent Service (BIS).
NOTE 1: This ETS does not specify any service aspects of a Syntax-based Videotex Service.
This ETS is applicable to all devices supporting the Bearer Independent Service on the upper side of the
Network Layer (NL) [cf. Clause 11]. In the context of this ETS, a device is either a Videotex Terminal (VT),
a Videotex Service Centre (VSC), a Videotex Access Point (VAP) or a Videotex Host (VH) [cf.
subclause 3.1].
NOTE 2: Depending on the lower layer communication type in use (in particular ISDN DTE/DTE,
ISDN DTE/DCE or PSTN), a separate standard is assumed to be applicable for the
respective lower layer protocols. For X.25 networks where a significant number of
resets are generated by the network or for other underlying lower layers, further study
may be needed.
NOTE 3: At the date of publication, ETS 300 079 is an exception to NOTE 2.
2 Normative references
This ETS incorporates by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed
hereafter. For dated references, subsequent amendments to or revisions of any of these publications
apply to this ETS only when incorporated in it by amendment or revision. For undated references, the
latest edition of the publication referred to applies.
[1] CCITT Recommendation F.300 (1988): "Videotex service".
[2] CCITT Recommendation T.51 (1988): "Coded character sets for telematic
services".
[3] CCITT Recommendation X.3 (1992): "Packet assembly disassembly facility
(PAD) in a public data network".
[4] CCITT Recommendation X.25 (1980): "Interface between data terminal
equipment (DTE) and data circuit-terminating equipment (DCE) for terminals
operating in the packet mode and connected to public data networks by
dedicated circuit".
[5] CCITT Recommendation X.25 (1984): "Interface between data terminal
equipment (DTE) and data circuit-terminating equipment (DCE) for terminals
operating in the packet mode and connected to public data networks by
dedicated circuit".
[6] CCITT Recommendation X.29 (1992): "Procedures for the exchange of control
information and user data between a packet assembly/disassembly (PAD)
facility and a packet mode DTE or another PAD".
[7] CCITT Recommendation X.121 (1988): "International numbering plan for public
data networks".
[8] ETS 300 072: "Terminal Equipment (TE); Videotex presentation layer protocol,
Videotex presentation layer data syntax".
[9] ETS 300 073: "Videotex presentation layer data syntax; Geometric Display
(CEPT Recommendation T/TE 06-02, Edinburgh 1988)".
[10] ETS 300 074: "Videotex presentation layer data syntax transparent data (CEPT
Recommendation T/TE 06-03, Edinburgh 1988)".

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ETS 300 223: January 1993
[11] ETS 300 075: "Terminal Equipment (TE); Videotex processable data".
[12] ETS 300 076 (1992): "Terminal Equipment (TE); Videotex, Terminal Facility
Identifier (TFI)".
[13] ETS 300 149: "Terminal Equipment (TE); Videotex, Audio syntax".
[14] ETS 300 177: "Terminal Equipment (TE); Videotex, Photographic syntax".
[15] CCITT Recommendation X.200: "Reference model of Open Systems
Interconnection for CCITT applications".
[16] ISO 7498: "Information processing systems - Open Systems Interconnection -
Basic Reference Model".
[17] ISO/IEC 8208 (1990): "Information technology - Data communications - X.25
Packet Layer Protocol for Data Terminal Equipment".
[18] ISO/IEC 8208 (1990) Addendum 3 (1991): "Information processing systems -
Data communications - X.25 Packet Layer Protocol for Data Terminal
Equipment - Addendum 3: Conformance requirements".
[19] ISO/TR 8509: "Information processing systems - Open Systems Interconnection
- Service conventions".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of this ETS, the following definitions apply:
Access Function: the functional entity which gives access to the Videotex Service. This entity is an
integral part of the Videotex Service.
Access Network: the network which provides the link between the Terminal Function and the Access
Function.
Application layer: see OSI Reference Model, CCITT Recommendation X.200 [15]/ISO 7498 [16].
Audio data: generic term for data which can be made audible (e.g., wave form encoded, phonetically
encoded).
Bearer Independent Service Access Point: point in an end system where the user of the Bearer
Independent Service (BIS) accesses the service.
Called BIS user: a BIS user with whom a calling BIS user wishes to establish a Network Connection
(NC).
Calling BIS user: a BIS user that initiates a NC establishment request.
Confirm: see Service Conventions standard, ISO/TR 8509 [19].
Data Circuit-terminating Equipment (DCE): see ISO/IEC 8208 [17] and CCITT Recommendation
X.25 [5].
Data Terminal Equipment (DTE): see ISO/IEC 8208 [17] and CCITT Recommendation X.25 [5].
Distributed Videotex Application: a Videotex Application which makes use of more than one Videotex
Host (VH).
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ETS 300 223: January 1993
Host Access Network (HAN): the network which provides the link between the Access Function and the
Host Function(s). It is an integral part of the Videotex Service and may be void.
Host Function: the abstraction of the Videotex Applications available in a particular Videotex Service.
In-band: all communication aspects related to CCITT Recommendation X.29 [6] (including Telematic
Commands) based procedures.
Indication: see Service Conventions standard, ISO/TR 8509 [19].
Logical Channel: see ISO/IEC 8208 [17] and CCITT Recommendation X.25 [5].
Multi-media communication: term used to indicate that both pictorial and audio data are exchanged.
Network Connection (NC): see OSI Reference Model, CCITT Recommendation
X.200 [15]/ISO 7498 [16].
Network Layer (NL): see OSI Reference Model, CCITT Recommendation X.200 [15]/ISO 7498 [16].
Network Service: see OSI Reference Model, CCITT Recommendation X.200 [15]/ISO 7498 [16].
Out-Band: all communication aspects related to procedures not being based on CCITT Recommendation
X.29 [6] (including Telematic Commands), e.g. in case of an ISDN the use of the D-Channel for B-
Channel establishment.
Packet Layer: see ISO/IEC 8208 [17] and CCITT Recommendation X.25 [5].
Pictorial data: generic term for data which can be displayed (e.g. alphamosaic, geometric, photographic).
Primitive: see Service Conventions standard, ISO/TR 8509 [19].
Request: see Service Conventions standard, ISO/TR 8509 [19].
Response: see Service Conventions standard, ISO/TR 8509 [19].
Telematic Command (TC): in the scope of this ETS, a Telematic Command is a specific service element
which is carried in a complete packet sequence of CCITT Recommendation X.25 Packet Layer Protocol
(PLP) DATA packets with the Q-bit set to 1. The first octet in the User Data field of the first packet of the
complete packet sequence carries a value which is reserved for Videotex (cf. draft CCITT
Recommendation X.29 (1992), "Telematic service message, Videotex").
Terminal Function: the abstraction of a functional entity which acts as a Videotex Terminal (VT).
Videotex Access Point (VAP): see CCITT Recommendation F.300 [1].
Videotex Application: see CCITT Recommendation F.300 [1].
Videotex External Host: see CCITT Recommendation F.300 [1].
Videotex Host (VH): this term describes a computer which offers one or more applications and/or
facilities. It can be represented through a Videotex Host Computer, an External Videotex Host or a
Videotex Service Centre (VSC).
Videotex Host Computer: see CCITT Recommendation F.300 [1].
Videotex Service (VS): see CCITT Recommendation F.300 [1].

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ETS 300 223: January 1993
Videotex Service Centre (VSC): see CCITT Recommendation F.300 [1].
NOTE: According to CCITT Recommendation F.300 [1], a Videotex Service Centre (VSC)
provides host and/or access functions, i.e. it may also act as a Videotex Access Point
(VAP).
Videotex Terminal (VT): see CCITT Recommendation F.300 [1].
Virtual Call (VC): see ISO/IEC 8208 [17] and CCITT Recommendation X.25 [5].
Virtual Circuit: see ISO/IEC 8208 [17] and CCITT Recommendation X.25 [5].
3.2 Abbreviations
For the purposes of this ETS, the following abbreviations apply:
AP Access Point
AU Access Unit
BIS Bearer Independent Service
CCITT International Telegraph and Telephone Consultative Committee
CD Call Deflection
CLIP Calling Line Identification Presentation
CLIR Calling Line Identification Restriction
DCE Data Circuit-terminating Equipment
DDI Direct Dialling In
DDU Dialogue Data Unit
DFK Definable Function Key
DTE Data Terminal Equipment
DU Data Unit
DXE either a DTE or a DCE
ETS European Telecommunication Standard
ETSI European Telecommunications Standards Institute
HAN Host Access Network
IB In-Band
ISDN Integrated Services Digital Network
ISO International Organization for Standardization
IVAP ISDN Syntax-based VAP
IVT ISDN Syntax-based VT
LC Logical Channel
LSB Least Significant Bit
M-bit More Data bit
MBS M-bit Sequence
MSB Most Significant Bit
MSN Multiple Subscriber Number
NC Network Connection
NL Network Layer
OB Out-Band
OSI Open Systems Interconnection
PAD Packet Assembly/Disassembly
PDN Public Data Network
PDU Protocol Data Unit
PH Packet Handler
PLP Packet Layer Protocol
PSPDN Packet Switched Public Data Network
PSTN Public Switched Telephone Network
Q-bit Qualifier bit
SBV Syntax-Based Videotex
SUB Subaddressing
TC Telematic Command
TCH Telematic Command Header
TCM Telematic Command Message
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ETS 300 223: January 1993
TDU Telesoftware DU
TFI Terminal Facility Identifier
TPD Transparent Processable Data
UUI User-to-User Information
UUS User-to-User Signalling
VAP Videotex Access Point
VC Virtual Call
VH Videotex Host
VPDE Videotex Presentation Data Element
VS Videotex Service
VSC Videotex Service Centre
VT Videotex Terminal
4 Overview
The main feature of a Syntax-based Videotex Terminal (VT) is the capability to access those Videotex
Services which are defined for and used in a Public Switched Telephone Network (PSTN) or Packet
Switched Public Data Network (PSPDN) environment using the CCITT Recommendation X.25 Packet
Layer Protocol (X.25/PLP) on an arbitrary access network.
More advanced Videotex Services may make use of additional features which are presented in the
following subclauses.
4.1 Direct selection of Videotex applications
The protocol allows the Videotex Terminal (VT) to shortcut the dialogue and welcome phase of the
Videotex Service and to be connected with a given Videotex Application identified by a network address or
a mnemonic.
4.2 Multi-communication
Multi-communication allows a terminal to establish several independent communication channels to one
or several independent Videotex Hosts or Videotex Applications.
The protocol supports multi-communication using several Network Connections (NCs).
NOTE 1: In the case of an ISDN, several Network connections may be provided using one
B-channel only.
NOTE 2: The handling of several independent communication channels may appear in any
configuration (cf. Annex A (informative)).
EXAMPLE: Assume that "ETSI" and "CCITT" are two Videotex Applications offering the
possibility to Videotex users to read texts of telecommunication standards. In
order to compare the text of a given ETS with an equivalent CCITT
Recommendation, the terminal should establish a network connection with each
of the two applications. The information from the two applications shall be
simultaneously displayed on the terminal using some windowing capability.
4.3 Multi-media communication
Multi-media information may contain pictorial data (i.e., alphamosaic, geometric, and photographic display
elements) and audio data. The audio data may be transmitted either in parallel or in serial with the pictorial
data.
When the audio data is transmitted in serial with the pictorial data, a single NC may be used to carry both.
When the audio data has to be sent in parallel with the pictorial data, a second NC dedicated to the
transmission of audio data shall be set up.

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ETS 300 223: January 1993
The protocol supports multi-media communication using several NCs, providing for the simultaneous
reproduction of both pictorial and audio information, in addition to a serial transmission already covered by
the data syntax.
NOTE 1: In the case of an ISDN, several NCs may be provided using one B-channel, only.
NOTE 2: The handling of several additional communication channels may appear in any
configuration (cf. Annex A (informative)).
4.4 Distributed Videotex application
It is recognised that, to accomplish some specific application, the application may be decomposed into
several sub-applications which may be implemented on more than one host. A communication channel
from the terminal to each of the sub-applications may exist. The incoming datastreams are combined in
the terminal to deliver the desired service to the user.
The protocol supports distributed Videotex applications using several NCs.
NOTE: In the case of an ISDN, several NCs may be provided using one B-channel, only.
EXAMPLE: Assume an application which serves PSTN terminals and ISDN terminals at the
same time. The PSTN application uses only alphamosaic information, while the
ISDN application additionally offers photographic pictures. The
"alphamosaic-host" is used for the dialogue with both PSTN and ISDN
terminals. When a specific picture has to be displayed, on request of the
"dialogue-host" a second Virtual Call (VC) is established between the ISDN
terminal and the "picture-host".
4.5 Supplementary services
In the case of an ISDN, the protocol allows for a use of several ISDN supplementary
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